Conventionally, there is known a closure member control device that uses a DC motor for driving and controlling a closure member of a vehicle, such as a windowpane or slide door. In such closure member control devices, it is required to stop or reverse the rotation of the motor when there is a pinching of a foreign object. In order to detect pinching of a foreign object, it is conceived to detect a motor load. The motor load can be obtained from the armature current and terminal voltage of the motor. However, the detection of electric current may require use of a current pick-up coil or a shunt resistor having a small resistance, and this would increase the number of component parts and thus increase the cost. For this reason, it is proposed to estimate the motor load from the motor voltage, angular speed and angular acceleration, and to determine that there is a pinching of a foreign object when a state of the estimated load being above a prescribed threshold value has continued for a prescribed time period (sometimes referred to as mask time) or longer (see Japanese Patent Application Laid-Open No. 2004-242425, for example).
In the above JPA Laid-Open No. 2004-242425, the estimated load P can be obtained by the following equation:P=Bm(ω0−ω)+(Tm−Tm0)−Jm·dω,  (1)
where Bm is a viscosity coefficient of motor internal load, ω is an angular speed, ω0 is a stationary angular speed with no outer load, Tm is a motor torque, Tm0 is a motor torque with no outer load, Jm is an inertial moment of the device (such as a window opening/closing device) inclusive of the motor, and dω is an angular acceleration.
In the above equation, the term (Tm−Tm0) can be divided into the voltage and angular speed terms to be expressed by the following equation:Tm=−a·ω+b·V+c,  (2)where a, b, c are constants specific to the motor. The equation (2) can be expressed in the form of a function or map for each motor and stored in a memory such as a ROM.
Using the equations (1) and (2), the estimated load P can be expressed as follows:P=(Bm+a)(ω0−ω)+b(V−V0)−Jm·dω,   (3)
where in the equation (3), (Bm+a) (ω0−ω) may be referred to as an angular speed difference computation term, b(V−V0) may be referred to as a voltage difference computation term, and Jm·dω may be referred to as an angular acceleration computation term (or inertia term).
In the pinching determination based on the estimated load as above, if a disturbance is caused during the closing operation of the closure member due to travel of the vehicle on a road with surface irregularities, for example, the angular speed ω and/or angular acceleration dω of the motor can change considerably, which can lead to a considerable change in the estimated load P and as a result, it may be erroneously determined that there is a pinched object when actually there is not. To solve such a problem, it has been proposed to vary the threshold value for pinching determination depending on the condition of the road (see Japanese Patent Application Laid-Open No. 9-328965, for example). In another publication, it is proposed to modify the threshold value for indicating a pinching of a foreign object so as to lower the pinching detection sensitivity when a disturbance is detected (see Japanese Patent Application Laid-Open No. 10-169310, for example). However, in order to eliminate the influence of oscillatory disturbance more effectively and achieve reliable pinching determination, a technique for more precise disturbance detection is needed.
Further, if a temporary large impact is imparted to the vehicle during the closing operation of the closure member, such as when a door is shut, the estimated load P can change abruptly, leading to an erroneous determination of pinching. It is proposed in Japanese Patent Application Laid-Open No. 9-125815 to increase the threshold value for pinching determination when a door closing action is detected by a door switch during an upward movement of the windowpane. However, the detection of door closing action using a door switch or the like can make the device complicated. Also, the increase in the threshold value may still result in an erroneous detection of pinching if there is a temporary large disturbance beyond the increased threshold value.
During the starting period of the motor, the motor operation tends to be unstable. Specifically, the angular speed ω and angular acceleration dω can vary in a wide range and erroneous pinching determination tends to happen. For this reason, the pinching detection and determination was not conducted during a prescribed period (mask period) from the start-up of the motor, but in the case that a foreign object is already caught at the start-up of the motor, the load when a determination is made that there is a pinched object tends to be excessively large because the pinching determination process is started after the mask period has lapsed (see Japanese Patent Application Laid-Open No. 2005-83052).
Further, the characteristics of the motors can differ for individual motors and can also change during the operable period, and thus in order to detect a pinching of an object reliably and quickly, it is necessary to take into consideration the motor characteristics differences depending on individual motors and their temporal change.
Yet further, in the case where it is determined that there is a foreign object pinching when a state that the estimated load is above a prescribed threshold value has continued for a prescribed period of time or longer, the load when the determination of pinching is made (referred to as “pinching load”) can be excessively large when the traveling speed of the closure member is fast (i.e., when the load increasing rate is large).